1. Field of the Invention
The present invention relates to an apparatus that irradiates an optical disk serving as a recording medium with light, and thus reads a signal recorded therein.
2. Description of Related Art
During a seek operation for making access to a track of an optical disk located away from a track thereof that is being played at the moment, optical disk apparatuses turn off a tracking servo, and then perform an operation for moving an optical pickup at high speed in the direction of the radius of the optical disk. Conventionally, at the time of this operation, an objective lens is supported only by the force exerted by a spring, because the tracking servo is in an off state at this time, and therefore the objective lens vibrates due to sudden acceleration of the optical pickup. This makes, for example, a focus servo become disengaged, or delays the start of the tracking servo, because the vibration of the objective lens is not stopped instantly after the optical pickup has been moved. This makes it difficult to perform high-speed seek and high-speed access.
Therefore, for example, Japanese Patent Application Laid-Open No. S60-151879 discloses an optical disk playback apparatus that can switch the output impedance of a drive circuit that drives a drive coil for use in driving an objective lens actuator. This apparatus makes the output impedance of the drive circuit lower when the optical pickup is moved, so that the vibration of the objective lens actuator is clamped and reduced with a back electromotive force of the drive coil. This makes it possible to reduce the seek time and the access time.
However, the above-described method is not very effective in reducing the vibration, although it somewhat reduces the vibration of the objective lens that occurs when the optical pickup is moved. Thus, for example, what is disclosed in Japanese Patent Application Laid-Open No. S59-84353 detects the amount of shift of an objective lens with a sensor that detects the amount of shift of the objective lens, or, instead of using the sensor, by using a tracking error signal and an RF signal based on the reflected light resulting from a beam reflected from an optical disk, so that the amount of shift of the objective lens is controlled to a certain value during an operation for moving an optical pickup at high speed in the direction of the radius of the optical disk. With this method, it is possible to reduce the vibration of the objective lens that occurs when the optical pickup is moved to almost zero.
However, the above-described method using a sensor requires installation of a sensor and an extra circuit for processing a signal from the sensor. This leads to higher costs.
Moreover, the above-described method using a tracking error signal and an RF signal has the following disadvantages. When an optical disk has an area where no RF signal is recorded, no RF signal is detected, and therefore it is impossible to detect the amount of shift. Thus, with this method, it is impossible to control the amount of shift of the objective lens of the optical disk having an area where no RF signal is recorded. Furthermore, processing or the like of the RF signal requires a highly complicated circuit. This leads to higher costs.